Direct firing thermal bend actuator ink jet printing mechanism

ABSTRACT

This patent describes an ink jet printer including a thermal actuator including a heater element encased within a material having a high coefficient of thermal expansion whereby the actuator operates by electrical heating the heater. The heater element has a corrugated structure so as to improve the thermal transfer to the actuation material so as to thereby increase the speed of actuation of the thermal actuator. The heater element is also of a serpentine or concertinaed form so as to allow substantially unhindered expansion of the actuation material. The thermal actuator can include layers sandwiched together where the conductor material has a series of slots or holes so as to allow the actuation material to be integrally joined together so as to reduce the likelihood of delamination of the layers.

CROSS REFERENCES TO RELATED APPLICATIONS

The following Australian provisional patent applications are herebyincorporated by cross-reference. For the purposes of location andidentification, US patent applications, identified by their US patentapplication serial numbers (USSN) are listed alongside the Australianapplications from which the US patent applications claim the right ofpriority.

CROSS-REFERENCED U.S. Patent/ AUSTRALIAN PATENT APPLICATION PROVISIONALPATENT (CLAIMING RIGHT OF PRIORITY FROM AUSTRALIAN APPLICATION NO.PROVISIONAL APPLICATION) DOCKET NO. PO7991 09/113,060 ART01 PO850509/113,070 ART02 PO7988 09/113,073 ART03 PO9395 09/112,748 ART04 PO801709/112,747 ART06 PO8014 09/112,776 ART07 PO8025 09/112,750 ART08 PO803209/112,746 ART09 PO7999 09/112,743 ART10 PO7998 09/112,742 ART11 PO803109/112,741 ART12 PO8030 09/112,740 ART13 PO7997 09/112,739 ART15 PO797909/113,053 ART16 PO8015 09/112,738 ART17 PO7978 09/113,067 ART18 PO798209/113,063 ART19 PO7989 09/113,069 ART20 PO8019 09/112,744 ART21 PO798009/113,058 ART22 PO8018 09/112,777 ART24 PO7938 09/113,224 ART25 PO801609/112,804 ART26 PO8024 09/112,805 ART27 PO7940 09/113,072 ART28 PO793909/112,785 ART29 PO8501 09/112,797 ART30 PO8500 09/112,796 ART31 PO794009/113,072 ART28 PO7939 09/112,785 ART29 PO8501 09/112,797 ART30 PO850009/112,796 ART31 PO7987 09/113,071 ART32 PO8022 09/112,824 ART33 PO849709/113,090 ART34 PO8020 09/112,823 ART38 PO8023 09/113,222 ART39 PO850409/112,786 ART42 PO8000 09/113,051 ART43 PO7977 09/112,782 ART44 PO793409/113,056 ART45 PO7990 09/113,059 ART46 PO8499 09/113,091 ART47 PO850209/112,753 ART48 PO7981 09/113,055 ART50 PO7986 09/113,057 ART51 PO798309/113,054 ART52 PO8026 09/112,752 ART53 PO8027 09/112,759 ART54 PO802809/112,757 ART56 PO9394 09/112,758 ART57 PO9396 09/113,107 ART58 PO939709/112,829 ART59 PO9398 09/112,792 ART60 PO9399 09/112,791 ART61 PO940009/112,790 ART62 PO9401 09/112,789 ART63 PO9402 09/112,788 ART64 PO940309/112,795 ART65 PO9405 09/112,749 ART66 PPO959 09/112,784 ART68 PP139709/112,783 ART69 PP2370 09/112,781 DOT01 PP2371 09/113,052 DOT02 PO800309/112,834 Fluid01 PO8005 09/113,103 Fluid02 PO9404 09/113,101 Fluid03PO8066 09/112,751 IJ01 PO8072 09/112,787 IJ02 PO8040 09/112,802 IJ03PO8071 09/112,803 IJ04 PO8047 09/113,097 IJ05 PO8035 09/113,099 IJ06PO8044 09/113,084 IJ07 PO8063 09/113,066 IJ08 PO8057 09/112,778 IJ09PO8056 09/112,779 IJ10 PO8069 09/113,077 IJ11 PO8049 09/113,061 1J12PO8036 09/112,818 1J13 PO8048 09/112,816 1J14 PO8070 09/112,772 IJ15PO8067 09/112,819 IJ16 PO8001 09/112,815 IJ17 PO8038 09/113,096 IJ18PO8033 09/113,068 IJ19 PO8002 09/113,095 IJ20 PO8068 09/112,808 IJ21PO8062 09/112,809 IJ22 PO8034 09/112,780 IJ23 PO8039 09/113,083 IJ24PO8041 09/113,121 IJ25 PO8004 09/113,122 IJ26 PO8037 09/112,793 IJ27PO8043 09/112,794 IJ28 PO8042 09/113,128 IJ29 PO8064 09/113,127 IJ30PO9389 09/112,756 IJ31 PO9391 09/112,755 IJ32 PP0888 09/112,754 IJ33PP0891 09/112,811 IJ34 PP0890 09/112,812 IJ35 PP0873 09/112,813 IJ36PP0993 09/112,814 IJ37 PP0890 09/112,764 IJ38 PP1398 09/112,765 IJ39PP2592 09/112,767 IJ40 PP2593 09/112,768 IJ41 PP3991 09/112,807 IJ42PP3987 09/112,806 IJ43 PP3985 09/112,820 IJ44 PP3983 09/112,821 IJ45PO7935 09/112,822 IJM01 PO7936 09/112,825 IJM02 PO7937 09/112,826 IJM03PO8061 09/112,827 IJM04 PO8054 09/112,828 IJM05 PO8065 09/113,111 IJM06PO8055 09/113,108 IJM07 PO8053 09/113,109 IJM08 PO8078 09/113,123 IJM09PO7933 09/113,114 IJM10 PO7950 09/113,115 IJM11 PO7949 09/113,129 IJM12PO8060 09/113,124 IJM13 PO8059 09/113,125 IJM14 PO8073 09/113,126 IJM15PO8076 09/113,119 IJM16 PO8075 09/113,120 IJM17 PO8079 09/113,221 IJM18PO8050 09/113,116 IJM19 PO8052 09/113,118 IJM20 PO7948 09/113,117 IJM21PO7951 09/113,113 IJM22 PO8074 09/113,130 IJM23 PO7941 09/113,110 IJM24PO8077 09/113,112 IJM25 PO8058 09/113,087 IJM26 PO8051 09/113,074 IJM27PO8045 09/113,089 IJM28 PO7952 09/113,088 IJM29 PO8046 09/112,771 IJM30PO9390 09/112,769 IJM31 PO9392 09/112,770 IJM32 PP0889 09/112,798 IJM35PP0887 09/112,801 IJM36 PP0882 09/112,800 IJM37 PP0874 09/112,799 IJM38PP1396 09/113,098 IJM39 PP3989 09/112,833 IJM40 PP2591 09/112,832 IJM41PP3990 09/112,831 IJM42 PP3986 09/112,830 IJM43 PP3984 09/112,836 IJM44PP3982 09/112,835 IJM45 PP0895 09/113,102 IR01 PP0870 09/113,106 IR02PP0869 09/113,105 IR04 PP0887 09/113,104 IR05 PP0885 09/112,810 IR06PP0884 09/112,766 IR10 PP0886 09/113,085 IR12 PP0871 09/113,086 IR13PP0876 09/113,094 IR14 PP0877 09/112,760 IR16 PP0878 09/112,773 IR17PP0879 09/112,774 IR18 PP0883 09/112,775 IR19 PP0880 09/112,745 IR20PP0881 09/113,092 IR21 PO8006 09/113,100 MEMS02 PO8007 09/113,093 MEMS03PO8008 09/113,062 MEMS04 PO8010 09/113,064 MEMS05 PO8011 09/113,082MEMS06 PO7947 09/113,081 MEMS07 PO7944 09/113,080 MEMS09 PO794609/113,079 MEMS10 PO9393 09/113,065 MEMS11 PP0875 09/113,078 MEMS12PP0894 09/113,075 MEMS13

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to ink jet printing and in particulardiscloses a direct firing thermal bend actuator ink jet printer.

The present invention further relates to the field of drop on demand inkjet printing.

BACKGROUND OF THE INVENTION

Many different types of printing have been invented, a large number ofwhich are presently in use. The known forms of print have a variety ofmethods for marking the print media with a relevant marking mediaCommonly used forms of printing include offset printing, laser printingand copying devices, dot matrix type impact printers, thermal paperprinters, film recorders, thermal wax printers, dye sublimation printersand ink jet printers both of the drop on demand and continuous flowtype. Each type of printer has its own advantages and problems whenconsidering cost, speed, quality, reliability, simplicity ofconstruction and operation etc.

In recent years, the field of ink jet printing, wherein each individualpixel of ink is derived from one or more ink nozzles has becomeincreasingly popular primarily due to its inexpensive and versatilenature.

Many different techniques on ink jet printing have been invented. For asurvey of the field, reference is made to an article by J Moore,“Non-Impact Printing: Introduction and Historical Perspective”, OutputHard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

Ink Jet printers themselves come in many different types. Theutilization of a continuous stream of ink in ink jet printing appears todate back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hanselldiscloses a simple form of continuous stream electro-static ink jetprinting.

U.S. Pat. No. 3,596,275 by Sweet also discloses a process of acontinuous ink jet printing including the step wherein the ink jetstream is modulated by a high frequency electro-static field so as tocause drop separation. This technique is still utilized by severalmanufacturers including Elmjet and Scitex (see also U.S. Pat. No.3,373,437 by Sweet et al).

Piezo-electric ink jet printers are also one form of commonly utilizedink jet printing device. Piezo-electric systems are disclosed by Kyseret. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragmmode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) whichdiscloses a squeeze mode of operation of a piezo electric crystal,Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode ofpiezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses aPiezo electric push mode actuation of the ink jet stream and Fischbeckin U.S. Pat. No. 4,584,590 which discloses a shear mode type ofpiezo-electric transducer element

Recently, thermal ink jet printing has become an extremely popular formof ink jet printing. The ink jet printing techniques include thosedisclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S.Pat. No. 4,490,728. Both the aforementioned references disclosed ink jetprinting techniques which rely upon the activation of an electrothermalactuator which results in the creation of a bubble in a constrictedspace, such as a nozzle, which thereby causes the ejection of ink froman aperture connected to the confined space onto a relevant print media.Printing devices utilizing the electro-thermal actuator are manufacturedby manufacturers such as Canon and Hewlett Packard.

As can be seen from the foregoing, many different types of printingtechnologies are available. Ideally, a printing technology should have anumber of desirable attributes. These include inexpensive constructionand operation, high speed operation, safe and continuous long termoperation etc. Each technology may have its own advantages anddisadvantages in the areas of cost, speed, quality, reliability, powerusage, simplicity of construction operation, durability and consumables.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an alternative formof actuation of ink drops for an ink jet printhead.

In accordance with the first aspect of the present invention there isprovided a nozzle arrangement which includes a thermal actuatorcomprising a heater element encased within a material having a highcoefficient of thermal expansion. The actuator operates by electricallyheating the heater element of the thermal actuator. The heater elementhas a corrugated structure so as to improve the thermal distribution ofheat from the heater element to the actuation material so as to increasethe speed of actuation of the thermal actuator. Further the heaterelement can be of a serpentine or concertina form so as to allowsubstantially unhindered expansion of the actuation material duringheating. The thermal actuator is utilized in an ink jet nozzle for theejection of ink from a nozzle chamber. Advantageously, both surfaces ofthe actuator are hydrophilic and the heater material within he actuatorcan comprise substantially copper. The hydrophilic material can beformed by means of suitable processing of a hydrophobic material.

In accordance with a second aspect of the current invention, there isprovided a thermal actuator comprising a heater element having a lowcoefficient of thermal expansion surrounded by an actuation materialhaving a high coefficient of thermal expansion wherein the thermalactuator includes first and second layers of actuation material and athird layer of conductive material, at least a portion of which isutilized as a heating element, wherein a portion of the conductormaterial has a series of slots or holes so as to allow the actuationmaterial to be integrally joined together so as to reduce the likelihoodof delamination of the layers. Thus a portion of the actuator includingslotted or holed conductor is stiff.

The stiff portion of the actuator can include a regularly spaced arrayof holes defined therein.

In accordance with a third aspect of the current invention, there isprovided an ink jet nozzle arrangement comprising the thermal actuatoras one wall of an ink chamber, wherein the thermal actuator is attachedto a wall of the nozzle chamber, and an ink chamber with an ejectionport for the ejection of ink in a wall opposite to the wall formed bythe thermal actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of thepresent invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

FIG. 1 is a cross-sectional view of a single ink jet nozzle constructedin accordance with the preferred embodiment, in its quiescent state;

FIG. 2 is a cross-sectional view of a single ink jet nozzle constructedin accordance with the preferred embodiment, in its activated state;

FIG. 3 is an exploded perspective view illustrating the construction ofa single ink jet nozzle in accordance with the preferred embodiment;

FIG. 4 is a cross-sectional schematic diagram illustrating theconstruction of a corrugated conductive layer in accordance with thepreferred embodiment of the present invention;

FIG. 5 is a schematic cross-sectional diagram illustrating thedevelopment of a resist material through a half-toned mask utilized inthe fabrication of a single ink jet nozzle in accordance with thepreferred embodiment;

FIG. 6 is a top view of the conductive layer only of the thermalactuator of a single ink jet nozzle constructed in accordance with thepreferred embodiment;

FIG. 7 provides a legend of the materials indicated in FIGS. 8 to 19;and

FIG. 8 to FIG. 19 illustrate sectional views of the manufacturing stepsin one form of construction of an ink jet printhead nozzle.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiment, ink is ejected from a nozzle arrangement bybending of a thermal actuator so as to eject ink.

Turning now to FIG. 1, there is illustrated a single nozzle arrangement1 of the preferred embodiment The nozzle arrangement 1 includes athermal actuator 2 located above a nozzle chamber 3 and an ink ejectionport 4. The thermal actuator 2 includes an electrical circuit comprisingleads 6, 7 connected to a serpentine resistive element 8. The resistiveelement 8 can comprise the copper layer in this respect, a copperstiffener 9 is provided to provide support for one end of the thermalactuator 2.

The copper resistive element 8 is constructed in a serpentine manner toprovide very little tensile strength along the length of the thermalactuator panel 2.

The copper resistive element 8 is embedded in a polytetrafluoroethylene(PTFE) layer 12. The PTFE layer 12 has a very high coefficient ofthermal expansion (approximately 770×10⁻⁶). This layer undergoes rapidexpansion when heated by the copper heater 8. The copper heater 8 ispositioned closer to a top surface of the PTFE layer 12, thereby heatingan upper layer of the PTFE layer 12 faster than the bottom layer,resulting in a bending down of the thermal actuator 2 towards theejection port 4.

The operation of the nozzle arrangement 1 is as follows:

1) When data signals distributed on the printhead indicate that thenozzle arrangement 1 is to eject a drop of ink, a drive transistor forthat the nozzle arrangement 1 is turned on. This energizes the leads 6,7, and the heater 8 in the actuator 2 for that the nozzle arrangement.The heater 8 is energized for approximately 3 μs, with the actualduration depending upon the design chosen for the nozzle arrangement.

2) The heater heats the PTFE layer 12, with the top layer of the PTFElayer 12 being heated more rapidly than the bottom layer. This causesthe actuator 2 to bend generally in the direction towards the ejectionport 4, in to the nozzle chamber 3, as illustrated in FIG. 2. Thebending of the actuator 2 pushes ink from the ink chamber 3 out of theejection port 4.

3) When the heater current is turned off, the actuator 2 begins toreturn to its quiescent position. The return of the actuator 2 ‘sucks’some of the ink back into the nozzle 4 into the nozzle chamber 3,causing an ink ligament connecting the ink drop to the ink in thechamber 3 to thin. The forward velocity of the drop and backwardvelocity of the ink in the chamber 3 are resolved by the ink dropbreaking off from the ink in the chamber 3. The ink drop then continuestowards the recording medium.

4) The actuator 2 remains at the quiescent position until the next dropejection cycle.

Construction

In order to construct a series of the nozzle arrangement 1, thefollowing major parts need to be constructed:

1) Drive circuitry to drive the nozzle arrangement 1.

2) The ejection port 4. The radius of the ejection port 4 is animportant determinant of drop velocity and drop size.

3) The actuator 2 is constructed of a heater layer 8 embedded in thePTFE layer 12. The actuator 2 is fixed at one side of the ink chamber 3,and the other end is suspended ‘over’ the ejection port 4. Approximatelyhalf of the actuator 2 contains the copper heater element 8. A heatingsection of the element 8 is proximate the fixed end of the actuator 2.

4) The nozzle chamber 3. The nozzle chamber 3 is slightly wider than theactuator 2. The gap 5 (SEE FIG. 1.) between the actuator 2 and thenozzle chamber 3 is determined by the fluid dynamics of the ink ejectionand refill process. If the gap is too large, much of the actuator forcewill be wasted on pushing ink around the edges of the actuator. If thegap is too small, the ink refill time will be too long. Also, if the gapis too small, the crystallographic etch of the nozzle chamber will taketoo long to complete. A 2 μm gap will usually be sufficient. The nozzlechamber is also deep enough so that air ingested through the ejectionport 4 when the actuator returns to its quiescent state does not extendto the actuator. If it does, the ingested bubble may form a cylindricalsurface instead of a hemispherical surface. If this happens, the chamber3 will not refill properly. A depth of approximately 20 μm is suitable.

5) Nozzle chamber ledges 13. As the actuator 2 moves approximately 10μm, and a crystallographic etch angle of chamber surface 14 is 54.74degrees, a gap of around 7 μm is required between the edge of the paddle2 and the outermost edge of the nozzle chamber 3. The walls of thenozzle chamber 3 must also clear the ejection port 4. This requires thatthe nozzle chamber 3 be approximately 52 μm wide, whereas the actuator 2is only 30 μm wide. Were there to be an 11 μm gap around the actuator 2,too much ink would flow around to the sides of the actuator 2 when theactuator 2 is energized. To prevent this, the nozzle chamber 3 isundercut 9 μm into the silicon surrounding the paddle, leaving a 9 μmnwide ledge 13 to prevent ink flow around the actuator 2.

EXAMPLE Basic Fabrication Sequence

Two wafers are required: a wafer upon which the active circuitry andnozzles are fabricated (the print head wafer) and a further wafer inwhich the ink channels are fabricated This is the ink channel wafer. Oneform of construction of printhead wafer will now be discussed withreference to FIG. 3 which illustrates an exploded perspective view of asingle ink jet nozzle constructed in accordance with the preferredembodiment.

1) Starting with a single crystal silicon wafer, which has a buriedepitaxial layer 16 of silicon which is heavily doped with boron. Theboron should be doped to preferably 10²⁰ atoms per cm³ of boron or more,and be approximately 3 μm thick The lightly doped silicon epitaxiallayer 15 on top of the boron doped layer should be approximately 8 μmthick, and be doped in a manner suitable for the active semiconductordevice technology chosen. This is the printhead wafer. The waferdiameter should preferably be the same as the ink channel wafer.

2) The drive transistors and data distribution circuitry layer 17 isfabricated according to the process chosen, up until the oxide layerover second level metal.

3) Next, a silicon nitride passivation layer 18 is deposited.

4) Next, the actuator 2 (FIG. 1) is constructed. The actuator 2comprises one copper layer 19 embedded into in a PTFE layer 20. Thecopper layer 19 comprises both the heater element 8 and a planar portion9 (of FIG. 1). Turning now to FIG. 4, the corrugated resistive elementcan be formed by depositing a resist layer 50 on top of the first PTFElayer 51. The resist layer 50 is exposed utilizing a mask 52 having ahalf-tone pattern delineating the corrugations. After development theresist 50 contains the corrugation pattern. The resist layer 50 and thePTFE layer 51 are then etched utilizing an etchant that erodes theresist layer 50 at substantially the same rate as the PTFE layer 51.This transfers the corrugated pattern into the PTFE layer 51. Turning toFIG. 5, on top of the corrugated PTFE layer 51 is deposited the copperheater layer 19 which takes on a corrugated form in accordance with itsunder layer. The copper heater layer 19 is then etched in a serpentineor concertina form. In FIG. 6 there is illustrated a top view of thecopper layer 19 only, comprising the serpentine heater element 8 and theportion 9. Subsequently, a further PTFE layer 53 is deposited on top oflayer 19 so as to form the top layer of the thermal actuator 2. Finally,the second PTFE layer 53 is planarized to form the top surface of thethermal actuator 2 (FIG. 1).

5) Etch through the PTFE, and all the way down to silicon in the regionaround the three sides of the paddle. The etched region should be etchedon all previous lithographic steps, so that the etch to silicon does notrequire strong selectivity against PTFE.

6) Etch the wafers in an anisotropic wet etch, which stops on <111>crystallographic planes or on heavily boron doped silicon. The etch canbe a batch wet etch in ethylenediamine pyrocatechol (EDP). The etchproceeds until the paddles are entirely undercut thereby forming thenozzle chamber 3. (SEE FIG. 1) The backside of the wafer need not beprotected against this etch, as the wafer is to be subsequently thinned.Approximately 60 μm of silicon will be etched from the wafer backsideduring this process.

7) Permanently bond the printhead wafer onto a pre-fabricated inkchannel wafer. The active side of the printhead wafer faces the inkchannel wafer. The ink channel wafer is attached to a backing plate, asit has already been etched into separate ink channel chips.

8) Etch the printhead wafer to entirely remove the backside silicon tothe level of the boron doped epitaxial layer 16. This etch can be abatch wet etch in ethylenediamine pyrocatechol (EDP).

9) Mask the an ejection port rim 11 (FIG. 1) from the underside of theprint head wafer. This mask is a series of circles approximately 0.5 μmto 1μm larger in radius than the nozzles. The purpose of this step is toleave a raised rim 11 around the ejection port 4, to help prevent inkspreading on the front surface of the wafer. This step can be eliminatedif the front surface is made sufficiently hydrophobic to reliablyprevent front surface wetting.

10) Etch the boron doped silicon layer 16 to a depth of 1 μm.

11) Mask the ejection ports from the underside of the printhead wafer.This mask can also include the chip edges.

12) Etch through the boron doped silicon layer to form the ink ejectionports 4.

13) Separate the chips from their backing plate. Each chip is now a fullprinthead including ink channels. The two wafers have already beenetched through, so the printheads do not need to be diced.

14) Test the printheads and TAB bond the good printheads.

15) Hydrophobize the front surface of the printheads.

17) Perform final testing on the TAB bonded printheads.

It would be evident to persons skilled in the relevant arts that thearrangement described by way of example in the preferred embodimentswill result in a nozzle arrangement able to eject ink on demand and besuitable for incorporation in a drop on demand ink jet printer devicehaving an array of nozzles for the ejection of ink on demand.

Of course, alternative embodiments will also be self-evident to theperson skilled in the art. For example, the thermal actuator could beoperated in a reverse mode wherein passing current through the actuatorresults in movement of the actuator to an ink loading position when thesubsequent cooling of the paddle results in the ink being ejected.However, this has a number of disadvantages in that cooling is likely totake a substantially longer time than heating and this arrangement wouldrequire a constant current to be passed through the nozzle arrangementwhen not in use.

One form of detailed manufacturing process which can be used tofabricate monolithic ink jet printheads operating in accordance with theprinciples taught by the present embodiment can proceed utilizing thefollowing steps:

1. Using a double sided polished wafer 60 deposit 3 microns of epitaxialsilicon heavily doped with boron 16.

2. Deposit 10 microns of epitaxial silicon 15, either p-type or n-type,depending upon the CMOS process used

3. Complete drive transistors, data distribution, and timing circuitsusing a 0.5 micron, one poly, 2 metal CMOS process 17. This step isshown in FIG. 8. For clarity, these diagrams may not be to scale, andmay not represent a cross section though any single plane of the nozzle.FIG. 7 is a key to representations of various materials in thesemanufacturing diagrams, and those of other cross referenced ink jetconfigurations.

4. Etch the CMOS oxide layers down to silicon or aluminum using Mask 1.This mask defines the nozzle chamber, and the edges of the printheadschips. This step is shown in FIG. 9.

5. Crystallographically etch the exposed silicon using, for example, KOHor EDP (ethylenediamine pyrocatechol). This etch stops on <111>crystallographic planes 61, and on the boron doped silicon buried layer.This step is shown in FIG. 10.

6. Deposit 0.5 microns of low stress silicon nitride 62.

7. Deposit 12 microns of sacrificial material 63 (polyimide). Planarizedown to nitride using CMP. The sacrificial material temporarily fillsthe nozzle cavity. This step is shown in FIG. 11.

8. Deposit 1 micron of PTFE 64.

9. Deposit, expose and develop 1 micron of resist 65 using Mask 2. Thismask is a gray-scale mask which defines the heater vias as well as thecorrugated PTFE surface that the heater is subsequently deposited on.

10. Etch the PTFE and resist at substantially the same rate. Thecorrugated resist thickness is transferred to the PTFE, and the PTFE iscompletely etched in the heater via positions. In the corrugatedregions, the resultant PTFE thickness nominally varies between 0.25micron and 0.75 micron, though exact values are not critical. This stepis shown in FIG. 12.

11. Etch the nitride and CMOS passivation down to second level metalusing the resist and PTFE as a mask.

12. Deposit and pattern resist using Mask 3. This mask defines theheater.

13. Deposit 0.5 microns of gold 66 (or other heater material with a lowYoung's modulus) and strip the resist. Steps 11 and 12 form a lift-offprocess. This step is shown in FIG. 13.

14. Deposit 1.5 microns of PTFE 67.

15. Etch the PTFE down to the nitride or sacrificial layer using Mask 4.This mask defines the actuator 2 and the bond pads. This step is shownin FIG. 14.

16. Wafer probe. All electrical connections are complete at this point,and the chips are not yet separated

17. Plasma process the PTFE to make the top and side surfaces of thepaddle hydrophilic. This allows the nozzle chamber to fill bycapillarity.

18. Mount the wafer on a glass blank 68 and back-etch the wafer usingKOH with no mask. This etch thins the wafer and stops at the buriedboron doped silicon layer. This step is shown in FIG. 15.

19. Plasma back-etch the boron doped silicon layer to a depth of 1micron using Mask 5. This mask defines the nozzle rim 11. This step isshown in FIG. 16.

20. Plasma back-etch through the boron doped layer and sacrificial layerusing Mask 6. This mask defines the nozzle 4, and the edge of the chips.At this stage, the chips are still mounted on the glass blank. This stepis shown in FIG. 17.

21. Etch the remaining sacrificial material while the wafer is stillattached to the glass blank.

22. Plasma process the PTFE through the nozzle holes to render the PTFEsurface hydrophilic.

23. Strip the adhesive layer to detach the chips from the glass blank.This process completely separates the chips. This step is shown in FIG.18.

24. Mount the printheads in their packaging, which may be a moldedplastic former incorporating ink channels which supply different colorsof ink to the appropriate regions of the front surface of the wafer.

25. Connect the printheads to their interconnect systems.

26. Hydrophobize the front surface of the printheads.

27. Fill with ink 69 and test the completed printheads. A filled nozzleis shown in FIG. 19.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiment without departing from the spirit orscope of the invention as broadly described. The present embodiment is,therefore, to be considered in all respects to be illustrative and notrestrictive.

The presently disclosed ink jet printing technology is potentiallysuited to a wide range of printing systems including: color andmonochrome office printers, short run digital printers, high speeddigital printers, offset press supplemental printers, low cost scanningprinters, high speed pagewidth printers, notebook computers within-built pagewidth printers, portable color and monochrome printers,color and monochrome copiers, color and monochrome facsimile machines,combined printer, facsimile and copying machines, label printers, largeformat plotters, photograph copiers, printers for digital photographic‘minilabs’, video printers, PHOTO CD (PHOTO CD is a registered trademark of the Eastman Kodak Company) printers, portable printers for PDAs,wallpaper printers, indoor sign printers, billboard printers, fabricprinters, camera printers and fault tolerant commercial printer arrays.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Ofcourse many different devices could be used. However presently popularink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption.This is approximately 100 times that required for high speed, and stemsfrom the energy-inefficient means of drop ejection. This involves therapid boiling of water to produce a vapor bubble which expels the ink.Water has a very high heat capacity, and must be superheated in thermalink jet applications. This leads to an efficiency of around 0.02%, fromelectricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size andcost. Piezoelectric crystals have a very small deflection at reasonabledrive voltages, and therefore require a large area for each nozzle.Also, each piezoelectric actuator must be connected to its drive circuiton a separate substrate. This is not a significant problem at thecurrent limit of around 300 nozzles per printhead, but is a majorimpediment to the fabrication of pagewidth printheads with 19,200nozzles.

Ideally, the ink jet technologies used meet the stringent requirementsof in-camera digital color printing and other high quality, high speed,low cost printing applications. To meet the requirements of digitalphotography, new ink jet technologies have been created. The targetfeatures include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systemsdescribed below with differing levels of difficulty. Forty-fivedifferent ink jet technologies have been developed by the Assignee togive a wide range of choices for high volume manufacture. Thesetechnologies form part of separate applications assigned to the presentAssignee as set out in the table below under the heading CrossReferences to Related Applications.

The ink jet designs shown here are suitable for a wide range of digitalprinting systems, from battery powered one-time use digital cameras,through to desktop and network printers, and through to commercialprinting systems.

For ease of manufacture using standard process equipment, the printheadis designed to be a monolithic 0.5 micron CMOS chip with MEMS postprocessing. For color photographic applications, the printhead is 100 mmlong, with a width which depends upon the ink jet type. The smallestprinthead designed is IJ38, which is 0.35 mm wide, giving a chip area of35 square mm. The printheads each contain 19,200 nozzles plus data andcontrol circuitry.

Ink is supplied to the back of the printhead by injection molded plasticink channels. The molding requires 50 micron features, which can becreated using a lithographically micromachined insert in a standardinjection molding tool. Ink flows through holes etched through the waferto the nozzle chambers fabricated on the front surface of the wafer. Theprinthead is connected to the camera circuitry by tape automatedbonding.

Tables of Drop-on-Demand Ink Jets

Eleven important characteristics of the fundamental operation ofindividual ink jet nozzles have been identified. These characteristicsare largely orthogonal, and so can be elucidated as an elevendimensional matrix. Most of the eleven axes of this matrix includeentries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of inkjet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains36.9 billion possible configurations of ink jet nozzle. While not all ofthe possible combinations result in a viable ink jet technology, manymillion configurations are viable. It is clearly impractical toelucidate all of the possible configurations. Instead, certain ink jettypes have been investigated in detail. These are designated IJ01 toIJ45 above which matches the docket numbers in the table under theheading Cross References to Related Applications.

Other ink jet configurations can readily be derived from theseforty-five examples by substituting alternative configurations along oneor more of the 11 axes. Most of the IJ01 to IJ45 examples can be madeinto ink jet print heads printheads with characteristics superior to anycurrently available ink jet technology.

Where there are prior art examples known to the inventor, one or more ofthese examples are listed in the examples column of the tables below.The IJ01 to IJ45 series are also listed in the examples column. In somecases, a print technology may be listed more than once in a table, whereit shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Homeprinters, Office network printers, Short run digital printers,Commercial print systems, Fabric printers, Pocket printers, Internet WWWprinters, Video printers, Medical imaging, Wide format printers,Notebook PC printers, Fax machines, Industrial printing systems,Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrixare set out in the following tables.

Description Advantages Disadvantages Examples ACTUATOR MECHANISM(APPLIED ONLY TO SELECTED INK DROPS) Thermal An electrothermal ♦ Largeforce ♦ High power ♦ Canon Bubblejet bubble heater heats the ink togenerated ♦ Ink carrier 1979 Endo et al GB above boiling point, ♦ Simplelimited to water patent 2,007,162 transferring significant construction♦ Low efficiency ♦ Xerox heater-in- heat to the aqueous ♦ No movingparts ♦ High pit 1990 Hawkins et ink. A bubble ♦ Fast operationtemperatures al U.S. Pat. No. 4,899,181 nucleates and quickly ♦ Smallchip area required ♦ Hewlett-Packard forms, expelling the required foractuator ♦ High mechanical TIJ 1982 Vaught et ink. stress al U.S. Pat.No. 4,490,728 The efficiency of the ♦ Unusual process is low, withmaterials required typically less than ♦ Large drive 0.05% of theelectrical transistors energy being ♦ Cavitation causes transformed intoactuator failure kinetic energy of the ♦ Kogation reduces drop. bubbleformation ♦ Large print heads are difficult to fabricate Piezo- Apiezoelectric crystal ♦ Low power ♦ Very large area ♦ Kyser et al U.S.Pat. electric such as lead consumption required for actuator No.3,946,398 lanthanum zirconate ♦ Many ink types ♦ Difficult to ♦ ZoltanU.S. Pat. No. (PZT) is electrically can be used integrate with 3,683,212activated, and either ♦ Fast operation electronics ♦ 1973 Stemmeexpands, shears, or ♦ High efficiency ♦ High voltage U.S. Pat. No.3,747,120 bends to apply drive transistors ♦ Epson Stylus pressure tothe ink, required ♦ Tektronix ejecting drops. ♦ Full pagewidth ♦ IJ04print heads impractical due to actuator size ♦ Requires electricalpoling in high field strengths during manufacture Electro- An electricfield is ♦ Low power ♦ Low maximum ♦ Seiko Epson, strictive used toactivate consumption strain (approx. Usui et all JP electrostriction in♦ Many ink types 0.01%) 253401/96 relaxor materials such can be used ♦Large area ♦ IJ04 as lead lanthanum ♦ Low thermal required for actuatorzirconate titanate expansion due to low strain (PLZT) or lead ♦ Electricfield ♦ Response speed magnesium niobate strength required is marginal(˜10 (PMN). (approx. 3.5 V/μm) μs) can be generated ♦ High voltagewithout difficulty drive transistors ♦ Does not require requiredelectrical poling ♦ Full pagewidth print heads impractical due toactuator size Ferro- An electric field is ♦ Low power ♦ Difficult to ♦IJ04 electric used to induce a phase consumption integrate withtransition between the ♦ Many ink types electronics antiferroelectric(AFE) can be used ♦ Unusual and ferroelectric (FE) ♦ Fast operationmaterials such as phase. Perovskite (<1 μs) PLZSnT are materials such astin ♦ Relatively high required modified lead longitudinal strain ♦Actuators require lanthanum zirconate ♦ High efficiency a large areatitanate (PLZSnT) ♦ Electric field exhibit large strains of strength ofaround 3 up to 1% associated V/μm can be readily with the AFE to FEprovided phase transition. Electro- Conductive plates are ♦ Low power ♦Difficult to ♦ IJ02, IJ04 static plates separated by a consumptionoperate electrostatic compressible or fluid ♦ Many ink types devices inan dielectric (usually air). can be used aqueous Upon application of a ♦Fast operation environment voltage, the plates ♦ The electrostaticattract each other and actuator will displace ink, causing normally needto be drop ejection. The separated from the conductive plates may ink bein a comb or ♦ Very large area honeycomb structure, required to achieveor stacked to increase high forces the surface area and ♦ High voltagetherefore the force. drive transistors may be required ♦ Full pagewidthprint heads are not competitive due to actuator size Electro- A strongelectric field ♦ Low current ♦ High voltage ♦ 1989 Saito et al, staticpull is applied to the ink, consumption required U.S. Pat. No. 4,799,068on ink whereupon ♦ Low temperature ♦ May be damaged ♦ 1989 Miura et al,electrostatic attraction by sparks due to air U.S. Pat. No. 4,810,954accelerates the ink breakdown ♦ Tone-jet towards the print ♦ Requiredfield medium. strength increases as the drop size decreases ♦ Highvoltage drive transistors required ♦ Electrostatic field attracts dustPermanent An electromagnet ♦ Low power ♦ Complex ♦ IJ07, IJ10 magnetdirectly attracts a consumption fabrication electro- permanent magnet, ♦Many ink types ♦ Permanent magnetic displacing ink and can be usedmagnetic material causing drop ejection. ♦ Fast operation such asNeodymium Rare earth magnets ♦ High efficiency Iron Boron (NdFeB) with afield strength ♦ Easy extension required. around 1 Tesla can be fromsingle nozzles ♦ High local used. Examples are: to pagewidth printcurrents required Samarium Cobalt heads ♦ Copper (SaCo) and magneticmetalization should materials in the be used for long neodymium ironboron electromigration family (NdFeB, lifetime and low NdDyFeBNb,resistivity NdDyFeB, etc) ♦ Pigmented inks are usually infeasible ♦Operating temperature limited to the Curie temperature (around 540 K.)Soft A solenoid induced a ♦ Low power ♦ Complex ♦ IJ01, IJ05, IJ08,magnetic magnetic field in a soft consumption fabrication IJ10, IJ12,IJ14, core electro- magnetic core or yoke ♦ Many ink types ♦ Materialsnot IJ15, IJ17 magnetic fabricated from a can be used usually present ina ferrous material such ♦ Fast operation CMOS fab such as aselectroplated iron ♦ High efficiency NiFe, CoNiFe, or alloys such asCoNiFe ♦ Easy extension CoFe are required [1], CoFe, or NiFe from singlenozzles ♦ High local alloys. Typically, the to pagewidth print currentsrequired soft magnetic material heads ♦ Copper is in two parts, whichmetalization should are normally held be used for long apart by aspring. electromigration When the solenoid is lifetime and low actuated,the two parts resistivity attract, displacing the ♦ Electroplating isink. required ♦ High saturation flux density is required (2.0-2.1 T isachievable with CoNiFe [1]) Lorenz The Lorenz force ♦ Low power ♦ Forceacts as a ♦ IJ06, IJ11, IJ13, force acting on a current consumptiontwisting motion IJ16 carrying wire in a ♦ Many ink types ♦ Typically,only a magnetic field is can be used quarter of the utilized. ♦ Fastoperation solenoid length This allows the ♦ High efficiency providesforce in a magnetic field to be ♦ Easy extension useful directionsupplied externally to from single nozzles ♦ High local the print head,for to pagewidth print currents required example with rare heads ♦Copper earth permanent metalization should magnets. be used for longOnly the current electromigration carrying wire need be lifetime and lowfabricated on the print- resistivity head, simplifying ♦ Pigmented inksmaterials are usually requirements. infeasible Magneto- The actuatoruses the ♦ Many ink types ♦ Force acts as a ♦ Fischenbeck, strictiongiant magnetostrictive can be used twisting motion U.S. Pat. No.4,032,929 effect of materials ♦ Fast operation ♦ Unusual ♦ IJ25 such asTerfenol-D (an ♦ Easy extension materials such as alloy of terbium, fromsingle nozzles Terfenol-D are dysprosium and iron to pagewidth printrequired developed at the Naval heads ♦ High local Ordnance Laboratory,♦ High force is currents required hence Ter-Fe-NOL). available ♦ CopperFor best efficiency, the metalization should actuator should be pre- beused for long stressed to approx. 8 electromigration MPa. lifetime andlow resistivity ♦ Pre-stressing may be required Surface Ink underpositive ♦ Low power ♦ Requires ♦ Silverbrook, EP tension pressure isheld in a consumption supplementary force 0771 658 A2 and reductionnozzle by surface ♦ Simple to effect drop related patent tension. Thesurface construction separation applications tension of the ink is ♦ Nounusual ♦ Requires special reduced below the materials required in inksurfactants bubble threshold, fabrication ♦ Speed may be causing the inkto ♦ High efficiency limited by surfactant egress from the ♦ Easyextension properties nozzle. from single nozzles to pagewidth printheads Viscosity The ink viscosity is ♦ Simple ♦ Requires ♦ Silverbrook,EP reduction locally reduced to construction supplementary force 0771658 A2 and select which drops are ♦ No unusual to effect drop relatedpatent to be ejected. A materials required in separation applicationsviscosity reduction can fabrication ♦ Requires special be achieved ♦Easy extension ink viscosity electrothermally with from single nozzlesproperties most inks, but special to pagewidth print ♦ High speed isinks can be engineered heads difficult to achieve for a 100:1 viscosity♦ Requires reduction. oscillating ink pressure ♦ A high temperaturedifference (typically 80 degrees) is required Acoustic An acoustic waveis ♦ Can operate ♦ Complex drive ♦ 1993 Hadimioglu generated and withouta nozzle circuitry et al, EUP 550,192 focussed upon the plate ♦ Complex♦ 1993 Elrod et al, drop ejection region. fabrication EUP 572,220 ♦ Lowefficiency ♦ Poor control of drop position ♦ Poor control of drop volumeThermo- An actuator which ♦ Low power ♦ Efficient aqueous ♦ IJ03, IJ09,IJ17, elastic bend relies upon differential consumption operationrequires a IJ18, IJ19, IJ20, actuator thermal expansion ♦ Many ink typesthermal insulator on IJ21, IJ22, IJ23, upon Joule heating is can be usedthe hot side IJ24, IJ27, IJ28, used. ♦ Simple planar ♦ Corrosion IJ29,IJ30, IJ31, fabrication prevention can be IJ32, IJ33, IJ34, ♦ Small chiparea difficult IJ35, IJ36, IJ37, required for each ♦ Pigmented inksIJ38, IJ39, IJ40, actuator may be infeasible, IJ41 ♦ Fast operation aspigment particles ♦ High efficiency may jam the bend ♦ CMOS actuatorcompatible voltages and currents ♦ Standard MEMS processes can be used ♦Easy extension from single nozzles to pagewidth print heads High CTE Amaterial with a very ♦ High force can ♦ Requires special ♦ IJ09, IJ17,IJI8, thermo- high coefficient of be generated material (e.g. PTFE)IJ20, IJ21, IJ22, elastic thermal expansion ♦ Three methods of ♦Requires a PTFE IJ23, IJ24, IJ27, actuator (CTE) such as PTFE depositionare deposition process, IJ28, IJ29, IJ30, polytetrafluoroethylene underdevelopment: which is not yet IJ31, IJ42, IJ43, (PTFE) is used. Aschemical vapor standard in ULSI IJ44 high CTE materials deposition(CVD), fabs are usually non- spin coating, and ♦ PTFE depositionconductive, a heater evaporation cannot be followed fabricated from a ♦PTFE is a with high conductive material is candidate for low temperature(above incorporated. A 50 μm dielectric constant 350° C.) processinglong PTFE bend insulation in ULSI ♦ Pigmented inks actuator with ♦ Verylow power may be infeasible; polysilicon heater and consumption aspigment particles 15 mW power input ♦ Many ink types may jam the bendcan provide 180 μN can be used actuator force and 10 μm ♦ Simple planardeflection. Actuator fabrication motions include: ♦ Small chip area Bendrequired for each Push actuator Buckle ♦ Fast operation Rotate ♦ Highefficiency ♦ CMOS compatible voltages and currents ♦ Easy extension fromsingle nozzles to pagewidth print heads Conductive A polymer with a high♦ High force can ♦ Requires special ♦ IJ24 polymer coefficient ofthermal be generated materials thermo- expansion (such as ♦ Very lowpower development (High elastic PTFE) is doped with consumption CTEconductive actuator conducting substances ♦ Many ink types polymer) toincrease its can be used ♦ Requires a PTFE conductivity to about 3 ♦Simple planar deposition process, orders of magnitude fabrication whichis not yet below that of copper. ♦ Small chip area standard in ULSI Theconducting required for each fabs polymer expands actuator ♦ PTFEdeposition when resistively ♦ Fast operation cannot be followed heated.♦ High efficiency with high Examples of ♦ CMOS temperature (aboveconducting dopants compatible voltages 350° C.) processing include: andcurrents ♦ Evaporation and Carbon nanotubes ♦ Easy extension CVDdeposition Metal fibers from single nozzles techniques cannot Conductivepolymers to pagewidth print be used such as doped heads ♦ Pigmented inkspolythiophene may be infeasible Carbon as pigment particles granules mayjam the bend actuator Shape A shape memory alloy ♦ High force is ♦Fatigue limits ♦ IJ26 memory such as TiNi (also available (stressesmaximum number alloy known as Nitinol- of hundreds of MPa) of cyclesNickel Titanium alloy ♦ Large strain is ♦ Low strain (1%) developed atthe Naval available (more than is required to extend OrdnanceLaboratory) 3%) fatigue resistance is thermally switched ♦ Highcorrosion ♦ Cycle rate between its weak resistance limited by heatmartensitic state and ♦ Simple removal its high stiffness construction ♦Requires unusual austenic state. The ♦ Easy extension materials (TiNi)shape of the actuator from single nozzles ♦ The latent heat of in itsmartensitic state to pagewidth print transformation must is deformedrelative to heads be provided the austenic shape. ♦ Low voltage ♦ Highcurrent The shape change operation operation causes ejection of a ♦Requires pre- drop. stressing to distort the martensitic state LinearLinear magnetic ♦ Linear Magnetic ♦ Requires unusual ♦ IJ12 Magneticactuators include the actuators can be semiconductor Actuator LinearInduction constructed with materials such as Actuator (LIA), Linear highthrust, long soft magnetic alloys Permanent Magnet travel, and high (e.gCoNiFe) Synchronous Actuator efficiency using ♦ Some varieties (LPMSA),Linear planar also require Reluctance semiconductor permanent magneticSynchronous Actuator fabrication materials such as (LRSA), Lineartechniques Neodymium iron Switched Reluctance ♦ Long actuator boron(NdFeB) Actuator (LSRA), and travel is available ♦ Requires the LinearStepper ♦ Medium force is complex multi- Actuator (LSA). available phasedrive circuitry ♦ Low voltage ♦ High current operation operation BASICOPERATION MODE Actuator This is the simplest ♦ Simple operation ♦ Droprepetition ♦ Thermal ink jet directly mode of operation: the ♦ Noexternal rate is usually ♦ Piezoelectric ink pushes ink actuatordirectly fields required limited to around 10 jet supplies sufficient ♦Satellite drops kHz. However, this ♦ IJ01, IJ02, IJ03, kinetic energy toexpel can be avoided if is not fundamental IJ04, IJ05, IJ06, the drop.The drop drop velocity is less to the method, but is IJ07, IJ09, IJ11,must have a sufficient than 4 m/s related to the refill IJ12, IJ14,IJ16, velocity to overcome ♦ Can be efficient, method normally IJ20,IJ22, IJ23, the surface tension. depending upon the used IJ24, IJ25,IJ26, actuator used ♦ All of the drop IJ27, IJ28, IJ29, kinetic energymust IJ30, IJ31, IJ32, be provided by the IJ33, IJ34, IJ35, actuatorIJ36, IJ37, IJ38, ♦ Satellite drops IJ39, IJ40, IJ41, usually form ifdrop IJ42, IJ43, IJ44 velocity is greater than 4.5 m/s Proximity Thedrops to be ♦ Very simple print ♦ Requires close ♦ Silverbrook, EPprinted are selected by head fabrication can proximity between 0771 658A2 and some manner (e.g. be used the print head and related patentthermally induced ♦ The drop the print media or applications surfacetension selection means transfer roller reduction of does not need to ♦May require two pressurized ink). provide the energy print headsprinting Selected drops are required to separate alternate rows of theseparated from the ink the drop from the image in the nozzle by nozzle ♦Monolithic color contact with the print print heads are medium or atransfer difficult roller. Electro- The drops to be ♦ Very simple print♦ Requires very ♦ Silverbrook, EP static pull printed are selected byhead fabrication can high electrostatic 0771 658 A2 and on ink somemanner (e.g. be used field related patent thermally induced ♦ The drop ♦Electrostatic field applications surface tension selection means forsmall nozzle ♦ Tone-Jet reduction of does not need to sizes is above airpressurized ink). provide the energy breakdown Selected drops arerequired to separate ♦ Electrostatic field separated from the ink thedrop from the may attract dust in the nozzle by a nozzle strong electricfield. Magnetic The drops to be ♦ Very simple print ♦ Requires ♦Silverbrook, EP pull on ink printed are selected by head fabrication canmagnetic ink 0771 658 A2 and some manner (e.g. be used ♦ Ink colorsother related patent thermally induced ♦ The drop than black areapplications surface tension selection means difficult reduction of doesnot need to ♦ Requires very pressurized ink). provide the energy highmagnetic fields Selected drops are required to separate separated fromthe ink the drop from the in the nozzle by a nozzle strong magneticfield acting on the magnetic ink. Shutter The actuator moves a ♦ Highspeed (>50 ♦ Moving parts are ♦ IJ13, IJ17, IJ21 shutter to block inkkHz) operation can required flow to the nozzle. The be achieved due to ♦Requires ink ink pressure is pulsed reduced refill time pressuremodulator at a multiple of the ♦ Drop timing can ♦ Friction and weardrop ejection be very accurate must be considered frequency. ♦ Theactuator ♦ Stiction is energy can be very possible low Shuttered Theactuator moves a ♦ Actuators with ♦ Moving parts are ♦ IJ08, IJ15, IJ18,grill shutter to block ink small travel can be required IJ19 flowthrough a grill to used ♦ Requires ink the nozzle. The shutter ♦Actuators with pressure modulator movement need only small force can be♦ Friction and wear be equal to the width used must be considered of thegrill holes. ♦ High speed (>50 ♦ Stiction is kHz) operation can possiblebe achieved Pulsed A pulsed magnetic ♦ Extremely low ♦ Requires an ♦IJ10 magnetic field attracts an ‘ink energy operation is external pulsedpull on ink pusher’ at the drop possible magnetic field pusher ejectionfrequency. An ♦ No heat ♦ Requires special actuator controls adissipation materials for both catch, which prevents problems theactuator and the the ink pusher from ink pusher moving when a drop is ♦Complex not to be ejected. construction AUXILIARY MECHANISM (APPLIED TOALL NOZZLES) None The actuator directly ♦ Simplicity of ♦ Drop ejection♦ Most ink jets, fires the ink drop, and construction energy must beincluding there is no external ♦ Simplicity of supplied by piezoelectricand field or other operation individual nozzle thermal bubble. mechanismrequired. ♦ Small physical actuator ♦ IJ01, IJ02, IJ03, size IJ04, IJ05,IJ07, IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, IJ27,IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, IJ39,IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating The ink pressure ♦ Oscillatingink ♦ Requires external ♦ Silverbrook, EP ink pressure oscillates,providing pressure can provide ink pressure 0771 658 A2 and (includingmuch of the drop a refill pulse, oscillator related patent acousticejection energy. The allowing higher ♦ Ink pressure applications stimul-actuator selects which operating speed phase and amplitude ♦ IJ08, IJ13,IJ15, ation) drops are to be fired ♦ The actuators must be carefullyIJ17, IJ18, IJ19, by selectively may operate with controlled IJ21blocking or enabling much lower energy ♦ Acoustic nozzles. The ink ♦Acoustic lenses reflections in the ink pressure oscillation can be usedto focus chamber must be may be achieved by the sound on the designedfor vibrating the print nozzles head, or preferably by an actuator inthe ink supply. Media The print head is ♦ Low power ♦ Precision ♦Silverbrook, EP proximity placed in close ♦ High accuracy assemblyrequired 0771 658 A2 and proximity to the print ♦ Simple print head ♦Paper fibers may related patent medium. Selected construction causeproblems applications drops protrude from ♦ Cannot print on the printhead further rough substrates than unselected drops, and contact theprint medium. The drop soaks into the medium fast enough to cause dropseparation. Transfer Drops are printed to a ♦ High accuracy ♦ Bulky ♦Silverbrook, EP roller transfer roller instead ♦ Wide range of ♦Expensive 0771 658 A2 and of straight to the print print substrates can♦ Complex related patent medium. A transfer be used constructionapplications roller can also be used ♦ Ink can be dried ♦ Tektronix hotfor proximity drop on the transfer roller melt piezoelectric separation.ink jet ♦ Any of the IJ series Electro- An electric field is ♦ Low power♦ Field strength ♦ Silverbrook, EP static used to accelerate ♦ Simpleprint head required for 0771 658 A2 and selected drops towardsconstruction separation of small related patent the print medium. dropsis near or applications above air ♦ Tone-Jet breakdown Direct A magneticfield is ♦ Low power ♦ Requires ♦ Silverbrook, EP magnetic used toaccelerate ♦ Simple print head magnetic ink 0771 658 A2 and fieldselected drops of construction ♦ Requires strong related patent magneticink towards magnetic field applications the print medium. Cross Theprint head is ♦ Does not require ♦ Requires external ♦ IJ06, IJ16magnetic placed in a constant magnetic materials magnet field magneticfield. The to be integrated in ♦ Current densities Lorenz force in a theprint head may be high, current carrying wire manufacturing resulting inis used to move the process electromigration actuator. problems Pulsed Apulsed magnetic ♦ Very low power ♦ Complex print ♦ IJ10 magnetic fieldis used to operation is possible head construction field cyclicallyattract a ♦ Small print head ♦ Magnetic paddle, which pushes sizematerials required in on the ink. A small print head actuator moves acatch, which selectively prevents the paddle from moving. ACTUATORAMPLIFICATION OR MODIFICATION METHOD None No actuator ♦ Operational ♦Many actuator ♦ Thermal Bubble mechanical simplicity mechanisms haveInkjet amplification is used. insufficient travel, ♦ IJ01, IJ02, IJ06,The actuator directly or insufficient force, IJ07, IJ16, IJ25, drivesthe drop to efficiently drive IJ26 ejection process. the drop ejectionprocess Differential An actuator material ♦ Provides greater ♦ Highstresses are ♦ Piezoelectric expansion expands more on one travel in areduced involved ♦ IJ03, IJ09, IJ17, bend side than on the other. printhead area ♦ Care must be IJ18, IJ19, IJ20, actuator The expansion may betaken that the IJ21, IJ22, IJ23, thermal, piezoelectric, materials donot IJ24, IJ27, IJ29, magnetostrictive, or delaminate IJ30, IJ31, IJ32,other mechanism. The ♦ Residual bend IJ33, IJ34, IJ35, bend actuatorconverts resulting from high IJ36, IJ37, IJ38, a high force low traveltemperature or high IJ39, IJ42, IJ43, actuator mechanism to stressduring IJ44 high travel, lower formation force mechanism. Transient Atrilayer bend ♦ Very good ♦ High stresses are ♦ IJ40, IJ41 bend actuatorwhere the two temperature stability involved actuator outside layers are♦ High speed, as a ♦ Care must be identical. This cancels new drop canbe taken that the bend due to ambient fired before heat materials do nottemperature and dissipates delaminate residual stress. The ♦ Cancelsresidual actuator only responds stress of formation to transient heatingof one side or the other. Reverse The actuator loads a ♦ Better coupling♦ Fabrication ♦ IJ05, IJ11 spring spring. When the to the ink complexityactuator is turned off, ♦ High stress in the the spring releases. springThis can reverse the force/distance curve of the actuator to make itcompatible with the force/time requirements of the drop ejection.Actuator A series of thin ♦ Increased travel ♦ Increased ♦ Some stackactuators are stacked. ♦ Reduced drive fabrication piezoelectric inkjets This can be voltage complexity ♦ IJ04 appropriate where ♦ Increasedactuators require high possibility of short electric field strength,circuits due to such as electrostatic pinholes and piezoelectricactuators. Multiple Multiple smaller ♦ Increases the ♦ Actuator forces ♦IJ12, IJ13, IJ18, actuators actuators are used force available from maynot add IJ20, IJ22, IJ28, simultaneously to an actuator linearly,reducing IJ42, IJ43 move the ink. Each ♦ Multiple efficiency actuatorneed provide actuators can be only a portion of the positioned tocontrol force required. ink flow accurately Linear A linear spring isused ♦ Matches low ♦ Requires print ♦ IJ15 Spring to transform a motiontravel actuator with head area for the with small travel and highertravel spring high force into a requirements longer travel, lower ♦Non-contact force motion. method of motion transformation Coiled A bendactuator is ♦ Increases travel ♦ Generally ♦ IJ17, IJ21, IJ34, actuatorcoiled to provide ♦ Reduces chip restricted to planar IJ35 greatertravel in a area implementations reduced chip area. ♦ Planar due toextreme implementations are fabrication difficulty relatively easy to inother orientations. fabricate. Flexure A bend actuator has a ♦ Simplemeans of ♦ Care must be ♦ IJ10, IJ19, IJ33 bend small region near theincreasing travel of taken not to exceed actuator fixture point, which abend actuator the elastic limit in flexes much more the flexure areareadily than the ♦ Stress remainder of the distribution is veryactuator. The actuator uneven flexing is effectively ♦ Difficult toconverted from an accurately model even coiling to an with finiteelement angular bend, resulting analysis in greater travel of theactuator tip. Catch The actuator controls a ♦ Very low ♦ Complex ♦ IJ10small catch. The catch actuator energy construction either enables or ♦Very small ♦ Requires external disables movement of actuator size forcean ink pusher that is ♦ Unsuitable for controlled in a bulk pigmentedinks manner. Gears Gears can be used to ♦ Low force, low ♦ Moving partsare ♦ IJ13 increase travel at the travel actuators can required expenseof duration. be used ♦ Several actuator Circular gears, rack ♦ Can befabricated cycles are required and pinion, ratchets, using standard ♦More complex and other gearing surface MEMS drive electronics methodscan be used. processes ♦ Complex construction ♦ Friction, friction, andwear are possible Buckle plate A buckle plate can be ♦ Very fast ♦ Muststay within ♦ S. Hirata et al, used to change a slow movement elasticlimits of the “An Ink-jet Head actuator into a fast achievable materialsfor long Using Diaphragm motion. It can also device life Microactuator”,convert a high force, ♦ High stresses Proc. IEEE MEMS, low travelactuator involved Feb. 1996, pp 418- into a high travel, ♦ Generallyhigh 423. medium force motion. power requirement ♦ IJ18, IJ27 Tapered Atapered magnetic ♦ Linearizes the ♦ Complex ♦ IJ14 magnetic pole canincrease magnetic construction pole travel at the expense force/distancecurve of force. Lever A lever and fulcrum is ♦ Matches low ♦ High stress♦ IJ32, IJ36, IJ37 used to transform a travel actuator with around thefulcrum motion with small higher travel travel and high forcerequirements into a motion with ♦ Fulcrum area has longer travel and nolinear movement, lower force. The lever and can be used for can alsoreverse the a fluid seal direction of travel. Rotary The actuator is ♦High mechanical ♦ Complex ♦ IJ28 impeller connected to a rotaryadvantage construction impeller. A small ♦ The ratio of force ♦Unsuitable for angular deflection of to travel of the pigmented inks theactuator results in actuator can be a rotation of the matched to theimpeller vanes, which nozzle requirements push the ink against byvarying the stationary vanes and number of impeller out of the nozzle.vanes Acoustic A refractive or ♦ No moving parts ♦ Large area ♦ 1993Hadimioglu lens diffractive (e.g. zone required et al, EUP 550,192plate) acoustic lens is ♦ Only relevant for ♦ 1993 Elrod et al, used toconcentrate acoustic ink jets EUP 572,220 sound waves. Sharp A sharppoint is used ♦ Simple ♦ Difficult to ♦ Tone-jet conductive toconcentrate an construction fabricate using point electrostatic field.standard VLSI processes for a surface ejecting ink- jet ♦ Only relevantfor electrostatic ink jets ACTUATOR MOTION Volume The volume of the ♦Simple ♦ High energy is ♦ Hewlett-Packard expansion actuator changes,construction in the typically required to Thermal Ink jet pushing theink in all case of thermal ink achieve volume ♦ Canon Bubblejetdirections. jet expansion. This leads to thermal stress, cavitation, andkogation in thermal ink jet implementations Linear, The actuator movesin ♦ Efficient ♦ High fabrication ♦ IJ01, IJ02, IJ04, normal to adirection normal to coupling to ink complexity may be IJ07, IJ11, IJ14chip surface the print head surface. drops ejected required to achieveThe nozzle is typically normal to the perpendicular in the line ofsurface motion movement. Parallel to The actuator moves ♦ Suitable for ♦Fabrication ♦ IJ12, IJ13, IJ15, chip surface parallel to the printplanar fabrication complexity IJ33, IJ34, IJ35, head surface. Drop ♦Friction IJ36 ejection may still be ♦ Stiction normal to the surface.Membrane An actuator with a ♦ The effective ♦ Fabrication ♦ 1982 Howkinspush high force but small area of the actuator complexity U.S. Pat. No.4,459,601 area is used to push a becomes the ♦ Actuator size stiffmembrane that is membrane area ♦ Difficulty of in contact with the ink.integration in a VLSI process Rotary The actuator causes ♦ Rotary levers♦ Device ♦ IJ05, IJ08, IJ13, the rotation of some may be used tocomplexity IJ28 element, such a grill or increase travel ♦ May haveimpeller ♦ Small chip area friction at a pivot requirements point BendThe actuator bends ♦ A very small ♦ Requires the ♦ 1970 Kyser et al whenenergized. This change in actuator to be made U.S. Pat. No. 3,946,398may be due to dimensions can be from at least two ♦ 1973 Stemmedifferential thermal converted to a large distinct layers, or to U.S.Pat. No. 3,747,120 expansion, motion. have a thermal ♦ IJ03, IJ09, IJ10,piezoelectric difference across the IJ19, IJ23, IJ24, expansion,actuator IJ25, IJ29, IJ30, magnetostriction, or IJ31, IJ33, IJ34, otherform of relative IJ35 dimensional change. Swivel The actuator swivels ♦Allows operation ♦ Inefficient ♦ IJ06 around a central pivot. where thenet linear coupling to the ink This motion is suitable force on thepaddle motion where there are is zero opposite forces ♦ Small chip areaapplied to opposite requirements sides of the paddle, e.g. Lorenz force.Straighten The actuator is ♦ Can be used with ♦ Requires careful ♦ IJ26,IJ32 normally bent, and shape memory balance of stresses straightenswhen alloys where the to ensure that the energized. austenic phase isquiescent bend is planar accurate Double The actuator bends in ♦ Oneactuator can ♦ Difficult to make ♦ IJ36, IJ37, IJ38 bend one directionwhen be used to power the drops ejected by one element is two nozzles.both bend directions energized, and bends ♦ Reduced chip identical. theother way when size. ♦ A small another element is ♦ Not sensitive toefficiency loss energized. ambient temperature compared to equivalentsingle bend actuators. Shear Energizing the ♦ Can increase the ♦ Notreadily ♦ 1985 Fishbeck actuator causes a shear effective travel ofapplicable to other U.S. Pat. No. 4,584,590 motion in the actuatorpiezoelectric actuator material. actuators mechanisms Radial con- Theactuator squeezes ♦ Relatively easy ♦ High force ♦ 1970 Zoltan U.S.striction an ink reservoir, to fabricate single required Pat. No.3,683,212 forcing ink from a nozzles from glass ♦ Inefficientconstricted nozzle. tubing as ♦ Difficult to macroscopic integrate withVLSI structures processes Coil/uncoil A coiled actuator ♦ Easy tofabricate ♦ Difficult to ♦ IJ17, IJ21, IJ34, uncoils or coils more as aplanar VLSI fabricate for non- IJ35 tightly. The motion of processplanar devices the free end of the ♦ Small area ♦ Poor out-of-planeactuator ejects the ink. required, therefore stiffness low cost Bow Theactuator bows (or ♦ Can increase the ♦ Maximum travel ♦ IJ16, IJ18, IJ27buckles) in the middle speed of travel is constrained when energized. ♦Mechanically ♦ High force rigid required Push-Pull Two actuators control♦ The structure is ♦ Not readily ♦ IJ18 a shutter. One actuator pinnedat both ends, suitable for ink jets pulls the shutter, and so has a highout-of- which directly push the other pushes it. plane rigidity the inkCurl A set of actuators curl ♦ Good fluid flow ♦ Design ♦ IJ20, IJ42inwards inwards to reduce the to the region behind complexity volume ofink that the actuator they enclose. increases efficiency Curl A set ofactuators curl ♦ Relatively simple ♦ Relatively large ♦ IJ43 outwardsoutwards, pressurizing construction chip area ink in a chambersurrounding the actuators, and expelling ink from a nozzle in thechamber. Iris Multiple vanes enclose ♦ High efficiency ♦ Highfabrication ♦ IJ22 a volume of ink. These ♦ Small chip area complexitysimultaneously rotate, ♦ Not suitable for reducing the volume pigmentedinks between the vanes. Acoustic The actuator vibrates ♦ The actuatorcan ♦ Large area ♦ 1993 Hadimioglu vibration at a high frequency. bephysically distant required for et al, EUP 550,192 from the inkefficient operation ♦ 1993 Elrod et al, at useful frequencies EUP572,220 ♦ Acoustic coupling and crosstalk ♦ Complex drive circuitry ♦Poor control of drop volume and position None In various ink jet ♦ Nomoving parts ♦ Various other ♦ Silverbrook, EP designs the actuatortradeoffs are 0771 658 A2 and does not move. required to related patenteliminate moving applications parts ♦ Tone-jet NOZZLE REFILL METHODSurface This is the normal way ♦ Fabrication ♦ Low speed ♦ Thermal inkjet tension that ink jets are simplicity ♦ Surface tension ♦Piezoelectric ink refilled. After the ♦ Operational force relatively jetactuator is energized, simplicity small compared to ♦ IJ01-IJ07, IJ10-it typically returns actuator force IJ14, IJ16, IJ20, rapidly to itsnormal ♦ Long refill time IJ22-IJ45 position. This rapid usuallydominates return sucks in air the total repetition through the nozzlerate opening. The ink surface tension at the nozzle then exerts a smallforce restoring the meniscus to a minimum area. This force refills thenozzle. Shuttered Ink to the nozzle ♦ High speed ♦ Requires ♦ IJ08,IJ13, IJ15, oscillating chamber is provided at ♦ Low actuator common inkIJ17, IJ18, IJ19, ink pressure a pressure that energy, as the pressureoscillator IJ21 oscillates at twice the actuator need only ♦ May not bedrop ejection open or close the suitable for frequency. When a shutter,instead of pigmented inks drop is to be ejected, ejecting the ink dropthe shutter is opened for 3 half cycles: drop ejection, actuator return,and refill. The shutter is then closed to prevent the nozzle chamberemptying during the next negative pressure cycle. Refill After the main♦ High speed, as ♦ Requires two ♦ IJ09 actuator actuator has ejected athe nozzle is independent drop a second (refill) actively refilledactuators per nozzle actuator is energized. The refill actuator pushesink into the nozzle chamber. The refill actuator returns slowly, toprevent its return from emptying the chamber again. Positive ink The inkis held a slight ♦ High refill rate, ♦ Surface spill ♦ Silverbrook, EPpressure positive pressure. therefore a high must be prevented 0771 658A2 and After the ink drop is drop repetition rate ♦ Highly relatedpatent ejected, the nozzle is possible hydrophobic print applicationschamber fills quickly head surfaces are ♦ Alternative for:, as surfacetension and required IJ01-IJ07, IJ10-IJ14, ink pressure both IJ16, IJ20,IJ22-IJ45 operate to refill the nozzle. METHOD OF RESTRICTING BACK-FLOWTHROUGH INLET Long inlet The ink inlet channel ♦ Design simplicity ♦Restricts refill ♦ Thermal ink jet channel to the nozzle chamber ♦Operational rate ♦ Piezoelectric ink is made long and simplicity ♦ Mayresult in a jet relatively narrow, ♦ Reduces relatively large chip ♦IJ42, IJ43 relying on viscous crosstalk area drag to reduce inlet ♦ Onlypartially back-flow. effective Positive ink The ink is under a ♦ Dropselection ♦ Requires a ♦ Silverbrook, EP pressure positive pressure, soand separation method (such as a 0771 658 A2 and that in the quiescentforces can be nozzle rim or related patent state some of the ink reducedeffective applications drop already protrudes ♦ Fast refill timehydrophobizing, or ♦ Possible from the nozzle. both) to preventoperation of the This reduces the flooding of the following: IJ01-pressure in the nozzle ejection surface of IJ07, IJ09-IJ12, chamberwhich is the print head. IJ14, IJ16, IJ20, required to eject a IJ22, ,IJ23-IJ34, certain volume of ink. IJ36-IJ41, IJ44 The reduction inchamber pressure results in a reduction in ink pushed out through theinlet. Baffle One or more baffles ♦ The refill rate is ♦ Design ♦ HPThermal Ink are placed in the inlet not as restricted as complexity Jetink flow. When the the long inlet ♦ May increase ♦ Tektronix actuator isenergized, method. fabrication piezoelectric ink jet the rapid ink ♦Reduces complexity (e.g. movement creates crosstalk Tektronix hot melteddies which restrict Piezoelectric print the flow through the heads).inlet. The slower refill process is unrestricted, and does not result ineddies. Flexible flap In this method recently ♦ Significantly ♦ Notapplicable to ♦ Canon restricts disclosed by Canon, reduces back-flowmost ink jet inlet the expanding actuator for edge-shooterconfigurations (bubble) pushes on a thermal ink jet ♦ Increased flexibleflap that devices fabrication restricts the inlet. complexity ♦Inelastic deformation of polymer flap results in creep over extended useInlet filter A filter is located ♦ Additional ♦ Restricts refill ♦ IJ04,IJ12, IJ24, between the ink inlet advantage of ink rate IJ27, IJ29, IJ30and the nozzle filtration ♦ May result in chamber. The filter ♦ Inkfilter may be complex has a multitude of fabricated with no constructionsmall holes or slots, additional process restricting ink flow. steps Thefilter also removes particles which may block the nozzle. Small inletThe ink inlet channel ♦ Design simplicity ♦ Restricts refill ♦ IJ02,IJ37, IJ44 compared to the nozzle chamber rate to nozzle has asubstantially ♦ May result in a smaller cross section relatively largechip than that of the nozzle, area resulting in easier ink ♦ Onlypartially egress out of the effective nozzle than out of the inlet.Inlet shutter A secondary actuator ♦ Increases speed ♦ Requires separate♦ IJ09 controls the position of of the ink-jet print refill actuator anda shutter, closing off head operation drive circuit the ink inlet whenthe main actuator is energized. The inlet is The method avoids the ♦Back-flow ♦ Requires careful ♦ IJ01, IJ03, IJ05, located problem ofinlet back- problem is design to minimize IJ06, IJ07, IJ10, behind theflow by arranging the eliminated the negative IJ11, IJ14, IJ16,ink-pushing ink-pushing surface of pressure behind the IJ22, IJ23, IJ25,surface the actuator between paddle IJ28, IJ31, IJ32, the inlet and theIJ33, IJ34, IJ35, nozzle. IJ36, IJ39, IJ40, IJ41 Part of the Theactuator and a ♦ Significant ♦ Small increase in ♦ IJ07, IJ20, IJ26,actuator wall of the ink reductions in back- fabrication IJ38 moves tochamber are arranged flow can be complexity shut off the so that themotion of achieved inlet the actuator closes off ♦ Compact designs theinlet. possible Nozzle In some configurations ♦ Ink back-flow ♦ Nonerelated to ♦ Silverbrook, EP actuator of ink jet, there is no problem isink back-flow on 0771 658 A2 and does not expansion or eliminatedactuation related patent result in ink movement of an applicationsback-flow actuator which may ♦ Valve-jet cause ink back-flow ♦ Tone-jetthrough the inlet. NOZZLE CLEARING METHOD Normal All of the nozzles are♦ No added ♦ May not be ♦ Most ink jet nozzle firing fired periodically,complexity on the sufficient to systems before the ink has a print headdisplace dried ink ♦ IJ01, IJ02, IJ03, chance to dry. When IJ04, IJ05,IJ06, not in use the nozzles IJ07, IJ09, IJ10, are sealed (capped) IJ11,IJ12, IJ14, against air. IJ16, IJ20, IJ22, The nozzle firing is IJ23,IJ24, IJ25, usually performed IJ26, IJ27, IJ28, during a special IJ29,IJ30, IJ31, clearing cycle, after IJ32, IJ33, IJ34, first moving theprint IJ36, IJ37, IJ38, head to a cleaning IJ39, IJ40, IJ41, station.IJ42, IJ43, IJ44, IJ45 Extra In systems which heat ♦ Can be highly ♦Requires higher ♦ Silverbrook, EP power to the ink, but do not boileffective if the drive voltage for 0771 658 A2 and ink heater it undernormal heater is adjacent to clearing related patent situations, nozzlethe nozzle ♦ May require applications clearing can be larger driveachieved by over- transistors powering the heater and boiling ink at thenozzle. Rapid The actuator is fired in ♦ Does not require ♦Effectiveness ♦ May be used succession rapid succession. In extra drivecircuits depends with: IJ01, IJ02, of actuator some configurations, onthe print head substantially upon IJ03, IJ04, IJ05, pulses this maycause heat ♦ Can be readily the configuration of IJ06, IJ07, IJ09,build-up at the nozzle controlled and the ink jet nozzle IJ10, IJ11,IJ14, which boils the ink, initiated by digital IJ16, IJ20, IJ22,clearing the nozzle. In logic IJ23, IJ24, IJ25, other situations, it mayIJ27, IJ28, IJ29, cause sufficient IJ30, IJ31, IJ32, vibrations todislodge IJ33, IJ34, IJ36, clogged nozzles. IJ37, IJ38, IJ39, IJ40,IJ41, IJ42, IJ43, IJ44, IJ45 Extra Where an actuator is ♦ A simple ♦ Notsuitable ♦ May be used power to not normally driven to solution wherewhere there is a with: IJ03, IJ09, ink pushing the limit of its motion,applicable hard limit to IJ16, IJ20, IJ23, actuator nozzle clearing maybe actuator movement IJ24, IJ25, IJ27, assisted by providing IJ29, IJ30,IJ31, an enhanced drive IJ32, IJ39, IJ40, signal to the actuator. IJ41,IJ42, IJ43, IJ44, IJ45 Acoustic An ultrasonic wave is ♦ A high nozzle ♦High ♦ IJ08, IJ13, IJ15, resonance applied to the ink clearingcapability implementation cost IJ17, IJ18, IJ19, chamber. This wave iscan be achieved if system does not IJ21 of an appropriate ♦ May bealready include an amplitude and implemented at very acoustic actuatorfrequency to cause low cost in systems sufficient force at the whichalready nozzle to clear include acoustic blockages. This is actuatorseasiest to achieve if the ultrasonic wave is at a resonant frequency ofthe ink cavity. Nozzle A microfabricated ♦ Can clear ♦ Accurate ♦Silverbrook, EP clearing plate is pushed against severely cloggedmechanical 0771 658 A2 and plate the nozzles. The plate nozzlesalignment is related patent has a post for every required applicationsnozzle. A post moves ♦ Moving parts are through each nozzle, requireddisplacing dried ink. ♦ There is risk of damage to the nozzles ♦Accurate fabrication is required Ink The pressure of the ink ♦ May beeffective ♦ Requires ♦ May be used pressure is temporarily where otherpressure pump or with all IJ series ink pulse increased so that inkmethods cannot be other pressure jets streams from all of the usedactuator nozzles. This may be ♦ Expensive used in conjunction ♦ Wastefulof ink with actuator energizing. Print head A flexible ‘blade’ is ♦Effective for ♦ Difficult to use if ♦ Many ink jet wiper wiped acrossthe print planar print head print head surface is systems head surface.The surfaces non-planar or very blade is usually ♦ Low cost fragilefabricated from a ♦ Requires flexible polymer, e.g. mechanical partsrubber or synthetic ♦ Blade can wear elastomer. out in high volume printsystems Separate A separate heater is ♦ Can be effective ♦ Fabrication ♦Can be used with ink boiling provided at the nozzle where other nozzlecomplexity many IJ series ink heater although the normal clearingmethods jets drop e-ection cannot be used mechanism does not ♦ Can berequire it. The heaters implemented at no do not require additional costin individual drive some ink jet circuits, as many configurationsnozzles can be cleared simultaneously, and no imaging is required.NOZZLE PLATE CONSTRUCTION Electro- A nozzle plate is ♦ Fabrication ♦High ♦ Hewlett Packard formed separately fabricated simplicitytemperatures and Thermal Ink jet nickel from electroformed pressures arenickel, and bonded to required to bond the print head chip. nozzle plate♦ Minimum thickness constraints ♦ Differential thermal expansion LaserIndividual nozzle ♦ No masks ♦ Each hole must ♦ Canon Bubblejet ablatedor holes are ablated by an required be individually ♦ 1988 Sercel etdrilled intense UV laser in a ♦ Can be quite fast formed al., SPIE, Vol.998 polymer nozzle plate, which is ♦ Some control ♦ Special Excimer Beamtypically a polymer over nozzle profile equipment required Applications,pp. such as polyimide or is possible ♦ Slow where there 76-83polysulphone ♦ Equipment are many thousands ♦ 1993 Watanabe required isrelatively of nozzles per print et al., U.S. Pat. No. low cost head5,208,604 ♦ May produce thin burrs at exit holes Silicon A separatenozzle ♦ High accuracy is ♦ Two part ♦ K. Bean, IEEE micro- plate isattainable construction Transactions on machined micromachined from ♦High cost Electron Devices, single crystal silicon, ♦ Requires Vol.ED-25, No. 10, and bonded to the precision alignment 1978, pp 1185-1195print head wafer. ♦ Nozzles may be ♦ Xerox 1990 clogged by adhesiveHawkins et al., U.S. Pat. No. 4,899,181 Glass Fine glass capillaries ♦No expensive ♦ Very small ♦ 1970 Zoltan U.S. Pat. capillaries are drawnfrom glass equipment required nozzle sizes are No. 3,683,212 tubing.This method ♦ Simple to make difficult to form has been used for singlenozzles ♦ Not suited for making individual mass production nozzles, butis difficult to use for bulk manufacturing of print heads with thousandsof nozzles. Monolithic, The nozzle plate is ♦ High accuracy ♦ Requires ♦Silverbrook, EP surface deposited as a layer (<1 μm) sacrificial layer0771 658 A2 and micro- using standard VLSI ♦ Monolithic under the nozzlerelated patent machined deposition techniques. ♦ Low cost plate to formthe applications using VLSI Nozzles are etched in ♦ Existing nozzlechamber ♦ IJ01, IJ02, IJ04, litho- the nozzle plate using processes canbe ♦ Surface may be IJ11, IJ12, IJ17, graphic VLSI lithography and usedfragile to the touch IJ18, IJ20, IJ22, processes etching. IJ24, IJ27,IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, IJ39, IJ40,IJ41, IJ42, IJ43, IJ44 Monolithic, The nozzle plate is a ♦ High accuracy♦ Requires long ♦ IJ03, IJ05, IJ06, etched buried etch stop in the (<1μm) etch times IJ07, IJ08, IJ09, through wafer. Nozzle ♦ Monolithic ♦Requires a IJ10, IJ13, IJ14, substrate chambers are etched in ♦ Low costsupport wafer IJ15, IJ16, IJ19, the front of the wafer, ♦ Nodifferential IJ21, IJ23, IJ25, and the wafer is expansion IJ26 thinnedfrom the back side. Nozzles are then etched in the etch stop layer. Nonozzle Various methods have ♦ No nozzles to ♦ Difficult to ♦ Ricoh 1995plate been tried to eliminate become clogged control drop Sekiya et alU.S. Pat. the nozzles entirely, to position accurately No. 5,412,413prevent nozzle ♦ Crosstalk ♦ 1993 Hadimioglu clogging. These problems etal EUP 550,192 include thermal bubble ♦ 1993 Elrod et al mechanisms andEUP 572,220 acoustic lens mechanisms Trough Each drop ejector has ♦Reduced ♦ Drop firing ♦ IJ35 a trough through manufacturing direction issensitive which a paddle moves. complexity to wicking. There is nonozzle ♦ Monolithic plate. Nozzle slit The elimination of ♦ No nozzlesto ♦ Difficult to ♦ 1989 Saito et al instead of nozzle holes and becomeclogged control drop U.S. Pat. No. 4,799,068 individual replacement by aslit position accurately nozzles encompassing many ♦ Crosstalk actuatorpositions problems reduces nozzle clogging, but increases crosstalk dueto ink surface waves DROP EJECTION DIRECTION Edge Ink flow is along the♦ Simple ♦ Nozzles limited ♦ Canon Bubblejet (‘edge surface of the chip,construction to edge 1979 Endo et al GB shooter’) and ink drops are ♦ Nosilicon ♦ High resolution patent 2,007,162 ejected from the chip etchingrequired is difficult ♦ Xerox heater-in- edge. ♦ Good heat ♦ Fast colorpit 1990 Hawkins et sinking via substrate printing requires al U.S. Pat.No. 4,899,181 ♦ Mechanically one print head per ♦ Tone-jet strong color♦ Ease of chip handing Surface Ink flow is along the ♦ No bulk silicon ♦Maximum ink ♦ Hewlett-Packard (‘roof surface of the chip, etchingrequired flow is severely TIJ 1982 Vaught et shooter’) and ink drops are♦ Silicon can make restricted al U.S. Pat. No. 4,490,728 ejected fromthe chip an effective heat ♦ IJ02, IJ11, IJ12, surface, normal to thesink IJ20, IJ22 plane of the chip. ♦ Mechanical strength Through Inkflow is through the ♦ High ink flow ♦ Requires bulk ♦ Silverbrook, EPchip, chip, and ink drops are ♦ Suitable for silicon etching 0771 658 A2and forward ejected from the front pagewidth print related patent (‘upsurface of the chip. heads applications shooter’) ♦ High nozzle ♦ IJ04,IJ17, IJ18, packing density IJ24, IJ27-IJ45 therefore low manufacturingcost Through Ink flow is through the ♦ High ink flow ♦ Requires wafer ♦IJ01, IJ03, IJ05, chip, chip, and ink drops are ♦ Suitable for thinningIJ06, IJ07, IJ08, reverse ejected from the rear pagewidth print ♦Requires special IJ09, IJ10, IJ13, (‘down surface of the chip. headshandling during IJ14, IJ15, IJ16, shooter’) ♦ High nozzle manufactureIJ19, IJ21, IJ23, packing density IJ25, IJ26 therefore low manufacturingcost Through Ink flow is through the ♦ Suitable for ♦ Pagewidth print ♦Epson Stylus actuator actuator, which is not piezoelectric print headsrequire ♦ Tektronix hot fabricated as part of heads several thousandmelt piezoelectric the same substrate as connections to drive ink jetsthe drive transistors. circuits ♦ Cannot be manufactured in standardCMOS fabs ♦ Complex assembly required INK TYPE Aqueous, Water based inkwhich ♦ Environmentally ♦ Slow drying ♦ Most existing ink dye typicallycontains: friendly ♦ Corrosive jets water, dye, surfactant, ♦ No odor ♦Bleeds on paper ♦ All IJ series ink humectant, and ♦ May jets biocide.strikethrough ♦ Silverbrook, EP Modern ink dyes have ♦ Cockles paper0771 658 A2 and high water-fastness, related patent light fastnessapplications Aqueous, Water based ink which ♦ Environmentally ♦ Slowdrying ♦ IJ02, IJ04, IJ21, pigment typically contains: friendly ♦Corrosive IJ26, IJ27, IJ30 water, pigment, ♦ No odor ♦ Pigment may ♦Silverbrook, EP surfactant, humectant, ♦ Reduced bleed clog nozzles 0771658 A2 and and biocide. ♦ Reduced wicking ♦ Pigment may related patentPigments have an ♦ Reduced clog actuator applications advantage inreduced strikethrough mechanisms ♦ Piezoelectric ink- bleed, wicking and♦ Cockles paper jets strikethrough. ♦ Thermal ink jets (with significantrestrictions) Methyl MEK is a highly ♦ Very fast drying ♦ Odorous ♦ AllIJ series ink Ethyl volatile solvent used ♦ Prints on various ♦Flammable jets Ketone for industrial printing substrates such as (MEK)on difficult surfaces metals and plastics such as aluminum cans. AlcoholAlcohol based inks ♦ Fast drying ♦ Slight odor ♦ All IJ series ink(ethanol, 2- can be used where the ♦ Operates at sub- ♦ Flammable jetsbutanol, printer must operate at freezing and others) temperatures belowtemperatures the freezing point of ♦ Reduced paper water. An example ofcockle this is in-camera ♦ Low cost consumer photographic printing.Phase The ink is solid at ♦ No drying time- ♦ High viscosity ♦ Tektronixhot change room temperature, and ink instantly freezes ♦ Printed inkmelt piezoelectric (hot melt) is melted in the print on the print mediumtypically has a ink jets head before jetting. ♦ Almost any print ‘waxy’feel ♦ 1989 Nowak Hot melt inks are medium can be used ♦ Printed pagesU.S. Pat. No. 4,820,346 usually wax based, ♦ No paper cockle may ‘block’♦ All IJ series ink with a melting point occurs ♦ Ink temperature jetsaround 80° C. After ♦ No wicking may be above the jetting the inkfreezes occurs curie point of almost instantly upon ♦ No bleed occurspermanent magnets contacting the print ♦ No strikethrough ♦ Ink heatersmedium or a transfer occurs consume power roller. ♦ Long warm-up timeOil Oil based inks are ♦ High solubility ♦ High viscosity: ♦ All IJseries ink extensively used in medium for some this is a significantjets offset printing. They dyes limitation for use in have advantages in♦ Does not cockle ink jets, which improved paper usually require acharacteristics on ♦ Does not wick low viscosity. Some paper (especiallyno through paper short chain and wicking or cockle). multi-branched oilsOil soluble dies and have a sufficiently pigments are required. lowviscosity. ♦ Slow drying Micro- A microemulsion is a ♦ Stops ink bleed ♦Viscosity higher ♦ All IJ series ink emulsion stable, self forming ♦High dye than water jets emulsion of oil, water, solubility ♦ Cost isslightly and surfactant. The ♦ Water, oil, and higher than watercharacteristic drop size amphiphilic soluble based ink is less than 100nm, dies can be used ♦ High surfactant and is determined by ♦ Canstabilize concentration the preferred curvature pigment required (aroundof the surfactant. suspensions 5%)

What is claimed is:
 1. A thermal actuator which comprises a heaterelement encased within a material having a high coefficient of thermalexpansion, said actuator operates by means of electrical heating by saidheater element of said thermal actuator wherein said heater element hasa corrugated structure so as to improve a thermal distribution of heatfrom said heater element to the material, the heater element beingpositioned within the material, closer to one of a pair of opposedsurfaces of the material than the other opposed surface, so thatexpansion of the material at the heater element, when the heater elementis energized, results in movement of the actuator.
 2. A thermal actuatoras claimed in claim 1 wherein the heater element is also of a serpentineor concertina form to allow substantially unhindered expansion of theactuation material during heating.
 3. A thermal actuator as claimed inclaim 1 wherein the actuator comprises part of an inkjet nozzlearrangement for ejecting ink from a nozzle chamber.
 4. A thermalactuator as claimed in claim 1 wherein surfaces of the actuator arehydrophilic.
 5. A thermal actuator as claimed in claim 1 wherein theheater element is substantially copper.
 6. A thermal actuator whichcomprises a heater element having a low coefficient of thermal expansionsurrounded by an actuation material having a high coefficient of thermalexpansion wherein said thermal actuator includes first and second layersof the actuation material and a third layer of conductive materialpositioned between the first and second layers of the actuationmaterial, at least a portion of the conductive material being utilizedas a heating element and wherein a remaining portion of the conductivematerial has a series of slots or holes so as to allow the first andsecond layers of the actuation material to be integrally joined togetherto reduce a likelihood of delamination of the layers, with one of thelayers being thinner than the other layer so that, when the heaterelement is energized, an extent of thermal expansion of the thinnerlayer is greater than that of the thicker layer, resulting in movementof the actuator.
 7. A thermal actuator as claimed in claim 6 wherein theremaining portion of the heater element having the series of slots orholes serves to stiffen the actuator.
 8. A thermal actuator as claimedin claim 7 wherein the remaining portion of the heater element includesa regularly spaced array of holes defined therein.
 9. A nozzlearrangement for an ink jet printer, the nozzle arrangement comprisingink chamber walls, which define an ink chamber; an ink ejection portdefined in one of the ink chamber walls; and a thermal actuator whichcomprises a heater element encased within a material having a highcoefficient of thermal expansion, whereby said actuator operates bymeans of electrical heating by said heater element of said thermalactuator wherein said heater element has a corrugated structure so as toimprove a thermal distribution of heat from said heater element to saidactuation material, the heater element being positioned within thematerial, closer to one of a pair of opposed surfaces of the materialthan the other opposed surface, so that expansion of the material at theheater element, when the heater element is energized, results inmovement of the actuator.
 10. A nozzle arrangement for an inkjetprinter, the nozzle arrangement comprising ink chamber walls, whichdefine an ink chamber; an ink ejection port defined in one of the inkchamber walls; and a thermal actuator which comprises a heater elementhaving a low coefficient of thermal expansion surrounded by an actuationmaterial having a high coefficient of thermal expansion wherein saidthermal actuator includes first and second layers of the actuationmaterial and a third layer of conductive material positioned between thefirst and second layers of the actuation material, at least a portion ofthe conductive material being utilized as a heating element and whereina remaining portion of the conductive material has a series of slots orholes so as to allow the first and second layers of the actuationmaterial to be integrally joined together to reduce a likelihood ofdelamination of the layers, with one of the layers being thinner thanthe other layer so that, when the heater element is energized, an extentof thermal expansion of the thinner layer is greater than that of thethicker layer, resulting in movement of the actuator.